THE EFFECTS OF HIPPOCAMPAL ASPIRATION LESIONS ON CONDITIONING TO THE CS AND TO A BACKGROUND STIMULUS IN TRACE CONDITIONED SUPPRESSION

Rats with hippocampal aspiration lesions or cortical control lesions w ere compared to sham operated controls in a trace conditioned suppress ion task, in which a long-lasting background stimulus played the role of more conventional contextual cues. In all three surgical treatment groups, conditioning to the explicit conditioned stimulus (CS) decreas ed, but conditioning to the background cue increased, when a longer tr ace interval was used. There was thus no evidence of a differential pa rtitioning of associative conditioning as a result of the lesion, desp ite the evident sensitivity of the behavioural paradigm to variations in the CS-->unconditioned stimulus (US) interval. This result contrast s with earlier reports using conventional contextual cues in analogous experimental designs, and so suggests that the sensitivity of context ual conditioning to hippocampal dysfunction depends at least in part o n the physical nature of conventional contextual cues, and not solely on the less precise predictive information that such cues typically pr ovide. (C) 1998 Elsevier Science B.V. All rights reserved.